According to the present invention, techniques for microfluidic systems, including a microfluidic chip or circuit, are provided. More particularly, the invention provides a microfluidic structure and method of manufacture, and a system and method for imaging a microfluidic device. Merely by way of example, the fiducial markings are used for processing and imaging a microfluidic chip, but it would be recognized that the invention has a much broader range of applicability.
Microfluidic techniques have progressed overtime. Certain techniques of producing microelectromechanical (MEMS) structures have been proposed. Such MEMS structures include pumps and valves. The pumps and valves are often silicon-based and are made from bulk micro-machining (which is a subtractive fabrication method whereby single crystal silicon is lithographically patterned and then etched to form three-dimensional structures). The pumps and valves also use surface micro-machining (which is an additive method where layers of semiconductor-type materials such as polysilicon, silicon nitride, silicon dioxide, and various metals are sequentially added and patterned to make three-dimensional structures). Unfortunately, certain limitations exist with these conventional MEMS structures and techniques for making them.
As merely an example, a limitation of silicon-based micro-machining is that the stiffness of the semiconductor materials used necessitates high actuation forces, which result in large and complex designs. In fact, both bulk and surface micro-machining methods are often limited by the stiffness of the materials used. Additionally, adhesion between various layers of the fabricated device is also a problem. For example, in bulk micro-machining, wafer bonding techniques must be employed to create multilayer structures. On the other hand, when surface micro-machining, thermal stresses between the various layers of the device limits the total device thickness, often to approximately 20 microns. Using either of the above methods, clean room fabrication and careful quality control are required.
Accordingly, techniques for manufacturing microfluidic systems using an elastomeric structure have been proposed. As merely an example, these structures are often made by forming an elastomeric layer on top of a micromachined mold. The micromachined mold has a raised protrusion which forms a recess extending along a bottom surface of the elastomeric layer. The elastomeric layer is bonded to other elastomeric layers to form fluid and control regions. The elastomeric layer has overcome certain limitations of conventional MEMS based structures. Further details of other characteristics of these elastomeric layers for microfluidic applications such as crystallization have been provided below.
Crystallization is an important technique to the biological and chemical arts. Specifically, a high-quality crystal of a target compound can be analyzed by x-ray diffraction techniques to produce an accurate three-dimensional structure of the target. This three-dimensional structure information can then be utilized to predict functionality and behavior of the target.
In theory, the crystallization process is simple. A target compound in pure form is dissolved in solvent. The chemical environment of the dissolved target material is then altered such that the target is less soluble and reverts to the solid phase in crystalline form. This change in chemical environment is typically accomplished by introducing a crystallizing agent that makes the target material less soluble, although changes in temperature and pressure can also influence solubility of the target material.
In practice however, forming a high quality crystal is generally difficult, often requiring much trial and error and patience on the part of the researcher. Specifically, the highly complex structure of even simple biological compounds means that they are usually not amenable to forming a highly ordered crystalline structure. Therefore, a researcher needs to be patient and methodical, experimenting with a large number of conditions for crystallization, altering parameters such as sample concentration, solvent type, countersolvent type, temperature, and duration in order to obtain a high quality crystal.
A high-throughput system for screening conditions for crystallization of target materials, for example proteins, is provided in a microfluidic device. The array of metering cells is formed by a multilayer elastomeric manufacturing process. Each metering cell comprises one or more of pairs of opposing chambers, each chamber being in fluid communication with the other through an interconnecting microfluidic channel, one chamber containing a protein solution, and the other, opposing chamber, containing a crystallization reagent. Along the channel, a valve is situated to keep the contents of opposing chambers from each other until the valve is opened, thus allowing free interface diffusion to occur between the opposing chambers through the interconnecting microfluidic channel. As the opposing chambers approach equilibrium with respect to crystallization reagent and protein concentrations as free interface diffusion progresses, the protein would at some point, form a crystal under certain conditions. In some embodiments, the microfluidic devices taught by Hansen et al. are have arrays of metering cells containing chambers for conducting protein crystallization experiments therein. Use of such arrays in turn provides for high-throughput testing of numerous conditions for protein crystallization which require analysis. See PCT publication WO 02/082047, published Oct. 17, 2002 and by Hansen, et al. PCT publication WO 02/082047 is incorporated by reference herein in its entirety for all purposes.
From the above, it is seen that improved techniques for elastomeric design and analysis are highly desirable.